The invention relates to a combined spring and shock absorber system for wheel suspensions or for axles of a vehicle using tubular rolling bellows arranged between a wheel-supporting or wheel-guide structure and a vehicle-body or vehicle body support structure, wherein the bellows space is filled with a fluid and communicates with a hydraulic accumulator.
When, in a hydraulic spring and shock absorber system, the suspension of a wheel is compressed, hydraulic fluid is displaced from the bellows space into the hydraulic accumulator through a throttle passage. In the process, a gas cushion is compressed in the hydraulic accumulator. As a result a counter-force is built up, which pushes the hydraulic fluid back out of the hydraulic accumulator through a throttle passage and into the bellows space.
When the suspension on one wheel is extended, the volume of the bellows space is increased. The pressure in the bellows space decreases. Due to the drop in pressure the hydraulic accumulator now causes hydraulic fluid to flow into the bellows space in a throttled fashion.
DE 100 24 571 discloses such a spring damping system. At high spring-extension speeds the internal pressure of the bellows space can decrease in an unacceptable fashion. At high spring-compression speeds there is a risk that the pressure in the bellows space will exceed a permissible upper limit.
It is the object of the present invention to provide a spring and shock absorber system in which the fluid pressure will not exceed any permissible limit value under high spring-extension and/or spring-compression speeds and wherein the operation of the spring and shock absorbing system is impaired as little as possible.
In a combined spring and shock absorber system for a wheel suspension of a vehicle comprising tubular rolling bellows arranged between a wheel-support structure and a vehicle body the bellows includes a space filled with a fluid in communication with a hydraulic accumulator. The bellows space is also in communication with at least one additional hydraulic accumulator via a throttle passage and via at least one pre-set differential pressure-control valve ensuring that threshold values for the internal pressure in the tubular rolling bellows are not exceeded in the event of high spring-extension and/or spring-compression speeds.
The additional hydraulic accumulator is arranged in parallel with the main hydraulic accumulator and also communicates with the bellows space through a throttle passage. It additionally includes the differential pressure-controlled valve. When the difference between the pressure in the bellows space and a pre-set pressure as determined for example by a spring exceeds a threshold value, the differential pressure-controlled valve opens. The threshold value is pre-set between an upper and a lower limiting value, for example a tubular rolling bellows-specific value. Hydraulic fluid now flows for example from the hydraulic accumulator into the bellows space, in order to counter a loss of volume during fast extension of the suspension. The hydraulic fluid is now conveyed rapidly and without throttling to the bellows space. As soon as the pre-set pressure difference is reached again, the differential-pressure-controlled valve closes again. This ensures that the internal pressure of the spring damping system remains within permissible pressure limits.
In order to avoid an overpressure and an under-pressure in the bellows space, it is possible, for example, to use two differential pressure-controlled valves on one hydraulic accumulator. One of these valves then opens when the pressure in the bellows space drops below a lower threshold value, the other when an upper threshold value is exceeded. These differential-pressure-controlled valves can also be combined with each other. It is also conceivable to use two separate hydraulic accumulators for these two tasks.
If the additional hydraulic accumulators fail, for example due to a leak, they can be switched off. The damping function of the spring damping system of the vehicle remains fully intact in the process.
The invention will become more readily apparent from the following description of embodiments thereof described below with reference to the accompanying drawings.